POPULATION DYNAMICS OF LAEONEREIS ACUTA (TREADWELL, 1923) (POLYCHAETA:NEREIDIDAE) FROM THE ENSEADA BEACH (S& Atilde;O SEBASTIÃO, SP, BRAZIL)
Omena, E. P. 1-2 & Amaral, C. Z. 2
1Dept.Biologia Marinha, IB/UFRJ, CEP:21941-570, Rio de Janeiro, RJ, Brazil
2Departamento de Zoologia, Instituto de Biologia, Universidade Estadual de Campinas, CP: 6109, 13089-970, Campinas, SP, Brazil Population dynamics and production of the polychaete Laeonereis acuta (Treadwell, 1923) were investigated in a tidal flat in southeastern Brazil (Enseada Beach, São Sebastião, SP, Brazil) between August 1995 and March 1997. Higher densities (3,500 ind/m2) were observed during the Summer months, mainly during March 1996 and February-March 1997. A sharp decrease of population density in Spring 1996 was observed. Probably, this change in population density was caused in part by the high temperatures and the desiccation caused by the extremely low diurnal tides which occurred during that period. Growth analysis was performed using computer based methods on lenght-frequency data (Elefan), yielding estimates of the growth parameters of the von Bertalanffy formula (VBGF). Two cohorts could be distinguished, one in December 1995 (with an equivalent cohort in December 1996) and another one in March 1996. The Summer cohorts (December 1995/1996) showed higher growth rates and shorter life span than the Autumn cohorts (March 1996). The life cycle of Laeonereis acuta appear to be greatly influenced by temperature regimes and food resources avaiability. The decrease of growth ratio which was observed before the reproduction period, is probably due to a higher energy allocation on gametogenesis over somatic growth during this period. The annual production of L. acuta on this tidal flat was 5.5 g AFDW/m2 and the production/biomass (P/B) ratio was 2.0. The results of the present study are discussed in relation to data collected during the preceeding year and as an expression of the presence of two cohorts.